I've said this before in other places, but to me it's not about number or length of time, but about mindset.
I'm taking this from another post I've made:
I personally think relapse versus struggling is subjective and depends more on the place your head is in. Are you wanting/trying to not self harm, or are you knowingly wanting to self harm and just doing it? To me if you are actively wanting not to or trying not to do the behavior, that's more indicative of just struggling. Where if you're just doing the behavior without really thinking or doing it because you want to self harm and don't care about trying to work on other ways to cope, that'd be more like a relapse.